[PATCH] selftests/mount_setattr: Fix failures on 64K PAGE_SIZE kernels

[Michael Ellerman <mpe@ellerman.id.au>]

Currently the mount_setattr_test fails on machines with a 64K PAGE_SIZE,
with errors such as:

  #  RUN           mount_setattr_idmapped.invalid_fd_negative ...
  mkfs.ext4: No space left on device while writing out and closing file system
  # mount_setattr_test.c:1055:invalid_fd_negative:Expected system("mkfs.ext4 -q /mnt/C/ext4.img") (256) == 0 (0)
  # invalid_fd_negative: Test terminated by assertion
  #          FAIL  mount_setattr_idmapped.invalid_fd_negative
  not ok 12 mount_setattr_idmapped.invalid_fd_negative

The code creates a 100,000 byte tmpfs:

	ASSERT_EQ(mount("testing", "/mnt", "tmpfs", MS_NOATIME | MS_NODEV,
			"size=100000,mode=700"), 0);

And then a little later creates a 2MB ext4 filesystem in that tmpfs:

	ASSERT_EQ(ftruncate(img_fd, 1024 * 2048), 0);
	ASSERT_EQ(system("mkfs.ext4 -q /mnt/C/ext4.img"), 0);

At first glance it seems like that should never work, after all 2MB is
larger than 100,000 bytes. However the filesystem image doesn't actually
occupy 2MB on "disk" (actually RAM, due to tmpfs). On 4K kernels the
ext4.img uses ~84KB of actual space (according to du), which just fits.

However on 64K PAGE_SIZE kernels the ext4.img takes at least 256KB,
which is too large to fit in the tmpfs, hence the errors.

It seems fraught to rely on the ext4.img taking less space on disk than
the allocated size, so instead create the tmpfs with a size of 2MB. With
that all 21 tests pass on 64K PAGE_SIZE kernels.

Fixes: 01eadc8dd96d ("tests: add mount_setattr() selftests")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 tools/testing/selftests/mount_setattr/mount_setattr_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mount_setattr/mount_setattr_test.c b/tools/testing/selftests/mount_setattr/mount_setattr_test.c
index 68801e1a9ec2..70f65eb320a7 100644
--- a/tools/testing/selftests/mount_setattr/mount_setattr_test.c
+++ b/tools/testing/selftests/mount_setattr/mount_setattr_test.c
@@ -1026,7 +1026,7 @@ FIXTURE_SETUP(mount_setattr_idmapped)
 			"size=100000,mode=700"), 0);
 
 	ASSERT_EQ(mount("testing", "/mnt", "tmpfs", MS_NOATIME | MS_NODEV,
-			"size=100000,mode=700"), 0);
+			"size=2m,mode=700"), 0);
 
 	ASSERT_EQ(mkdir("/mnt/A", 0777), 0);
 
-- 
2.47.0